Moving electrode electrostatic particle precipitator

ABSTRACT

An electrostatic particle precipitator includes a plurality of planar arrays of wire positioned in a stream of gas containing particles, the arrays of wire forming one electrode of a corona discharge device. A pair of endless roller chains supported by a plurality of sprocket wheels pass between the wire arrays. A plurality of grounded metallic plates that are generally rectangular in shape are detachably mounted on the roller chains such that the longer dimension is parallel to the gas stream and the shorter dimension is parallel to the direction of the motion of the chains. The plurality of plates form a moving collecting electrode. The moving electrode passes out of the gas stream and through a region wherein the individual plates are cleaned. The surface of the plates may include a plurality of depressed and raised areas to assist in collecting the particles.

United States Patent [191 Trump et a1.

[ MOVING ELECTRODE ELECTROSTATIC PARTICLE PRECIPITATOR [75] Inventors:John G. Trump, Winchester;

Helmut I. Milde, Andover, both of Mass.

[73] Assignee: High Voltage Engineering Corporation, Burlington, Mass.

[22] Filed: I Apr. 6, 1973 [21] Appl. No.: 348,743

[52] US. Cl. 55/149; 55/112; 55/114; 55/154 [51] Int. Cl. B03C 3/10 [58]Field of Search 55/113, 114, 115, 116, 55/149,l2l,14,l3,1l2,117,118,119,120, 154

[56] References Cited UNITED STATES PATENTS 2,212,885 8/1940 Pound et a155/116 2,383,111 8/1945 Dahlman 55/138 X 2,625,238 1/1953 Roper 55/114 X2,786,575 3/1957 Roberts 209/127 2,946,400 7/1960 Gustafsson .1 55/ 1563,008,541 11/1961 Wachter 55/149 X 3,028,714 4/1962 Mayer 55/1143,362,135 1/1968 Steuernagel 55/154 3,375,638 4/1968 Dungler 55/131 X3,581,468 6/1971 Gourdine et al.. 55/129 X 3,701,236 10/1971 Rotsky etal. 55/121 X [4 1 Oct. 14, 1975 3,740,925 6/1973 Gothard 55/113 XFOREIGN PATENTS OR APPLICATIONS 513,836 11/1920 France 55/149 377,7887/1964 Switzerland 55/149 OTHER PUBLICATIONS German Printed ApplicationNo. 1,001,973, printed 2-7-57, 1 sheet drawing, 2 pages specification.

Primary Examiner-Bernard Nozick Attorney, Agent, or FirmRussell & Nields[5 7] ABSTRACT An electrostatic particle precipitator includes aplurality of planar arrays of wire positioned in a stream of gascontaining particles, the arrays of wire forming one electrode of acorona discharge device. A pair of endless roller chains supported by aplurality of sprocket wheels pass between the wire arrays. A pluralityof grounded metallic plates that are generally rectangular in shape aredetachably mounted on the roller chains such that the longer dimensionis parallel to the gas stream and the shorter dimension is parallel tothe direction ofthe motion of the chains. The plurality of plates form amoving collecting electrode. The moving electrode passes out of the gasstream and through a region wherein the individual plates are cleaned.The surface of the plates may include a plurality of depressed andraised areas to assist in collecting the particles.

7 Claims, 17 Drawing Figures U.S.' Patent VOLFAGE SOURCE Oct. 14, 1975U.S. Patent Oct. 14, 1975 Sheet 2 of 4 Sheet 4 of 4 3,912,467

U.S. Patent Oct. 14, 1975 MOVING ELECTRODE ELECTROSTATIC PARTICLEPRECIPITATOR BACKGRO UND OF THE INVENTION The present invention relatesto electrostatic particle precipitators and more particularly, to aprecipitator having a moving collecting electrode.

Electrostatic precipitators have long been used for removing particlesfrom a gas. Basically, a corona discharge between a corona and acollecting electrode creates ions that adhere to the particles, therebycharging them. The forces resulting from the presence of chargedparticles in an electric field propel the particles to the collectingelectrode.

Those skilled in the art of electrostatic particle precipitators havelong struggled with the problem of removing and collecting the solidmaterials accumulated on the collecting electrode without causing thematerial to be re -entrained in the gas. Stationary collectingelectrodes that are mechanically vibrated have been tried, but they havea serious re-entrainment limitation because not all the material fallsdue to gravity into a collecting vessel. Since the electrode is in theregion of the gas, a significant quantity of the material becomesentrained in the gas, thereby seriously degrading precipitatorefficiency.

Concern over re-entrainment has led to efforts to have a movingcollecting electrode that is cleaned in a region outside the gas stream.Particle re-entrainment is thus reduced because the materials removedfrom the electrodes may not be swept into the gas stream.

One conventional moving electrode precipitator includes an endlessmetallic band that passes over vertically disposed sprockets to permitthe band to have approximately sinuous motion. The corona electrodes aredisposed adjacent the band. The band moves through a region outside thegas stream that applies a cleaning fluid to the band, brushes the band,dries the band and finally applies an adhesive to the band.

While this moving electrode precipitator was generally successful inreducing the re-entrainment problem, several problems arose clue to thenature of the moving electrode. Because of the presence of moving parts,there was greater chance of mechanical breakdown. Since the band was asingle entity, the entire precipitator had to be shut down if any partof the band required maintenance. Furthermore, the flexibility of theband can cause the particles to become loose where the band passes overthe sprockets. The smoothness of the band also necessitates theapplication of an adhesive to assist in securing the particle to theelectrode.

Thus, a particle precipitator that would reduce reentrainment, while atthe same time would eliminate the disadvantages of known movingelectrode precipitators, would be a valuable contribution to the art ofprecipitators.

SUMMARY OF THE INVENTION There is provided in accordance with thepresent invention an electrostatic particle precipitator that overcomesthe problems previously mentioned. More par ticularly, the precipitatorof the type with which the invention is concerned includes a pluralityof planar arrays of wire positioned in a stream of a fluid containingparticles, a plurality of plates positioned adjacent one another andadapted to be positioned between the arrays of wire, the plates formingthe collecting electrode, a device for producing a corona discharge anda device for moving the electrode around an endless path. Preferably, anapparatus is provided for cleaning the plates in a region outside thegas stream. The plates may then be separately and successionallycleaned.

There are several advantages to the collecting electrode being formed ofa plurality of plates following an endless path. The collectingelectrode may be cleaned more efficiently because each plate isseparately and successionally cleaned. The plates are preferablyseparated by a small space in the direction of movement to avoid contactof the plates with each other. Thus, the plates do not cause particlesto become loose when the belt passes around the sprocket wheels. Theplates are detachably mounted on a roller chain to allow rapid repair ofthe collecting electrode.

The plates may have depressed and raised areas on the collecting surfaceto enhance the collecting of the particles. The combined effect of theareas is to create in the depressed areas a zone that is protected fromthe forces of the moving gas stream and that has a low electric field.Charged particles tend to steer into low field regions. The plates maybe formed with rows and columns of alternately raised and lowered areas,the areas being circular, generally rectangular or square. Additionally,plates may have a plurality of flanges mounted thereon. The collectingplate may also have vectored or undulating sides or be formed as a solidmaterial or as a hollow tube, the solid or hollow configuration beingformed with holes through the thickness of the plate.

The cleaning device may include brushes, a heater, a vibrator, air jetsor liquid jets.

BRIEF DESCRIPTION OF THE DRAWINGS In the Drawings:

FIG. 1 is a perspective view of an electrostatic particle precipitatorarranged according to the present invention;

FIG. 2 is a perspective view of a modified form of a collectingelectrode plate having raised and depressed areas of square shape;

FIG. 3 is a perspective view of another form of a collecting electrodeplate having raised and depressed areas of circular shape;

FIG. 4a is an elevational view of another form of a collecting electrodeplate having raised and depressed areas of generally rectangular shape;

FIG. 4b is an alternative form of the collecting electrode plate shownin FIG. 4a,-

FIG. 5 is a perspective view of another form of a collecting electrodeplate having end flanges;

FIG. 6 is a perspective view of another form of a collecting electrodeplate having a plurality of flanges;

FIG. 7 is a diagram showing the connection of the wire electrodes to avoltage source;

FIG. 8a is a diagram of a brush for cleaning the plates;

FIG. 8b is a diagram of a heating device for cleaning the plates;

FIG. 8c is a diagram of a vibrator for cleaning the plates;

FIG. 8d is a diagram of air jets for cleaning the plates;

FIG. Se is a diagram of liquid jets for cleaning the plates;

FIG. 9 is a view of an alternate form of collecting plate havingvectored sides;

FIG. is a view of another alternate form of collecting plate havingundulating side portions;

FIG. 11 is a view of another form of collecting plate having holesformed therethrough;

FIG. 12 is a view of a collecting plate formed into a hollow tube withholes formed therein.

DESCRIPTION OF PREFERRED EMBODIMENTS In an exemplary embodiment of anelectrostatic particle precipitator arranged accordingly to the presentinvention, as shown in FIG. 1, a precipitator, represented generally bythe reference numeral 10, is disposed in the path of a stream of gasflowing in the direction of an arrow 12. The precipitator 10 is suitedfor removing particles from waste gases from coal and fuel powergenerating stations but it may also be used for many other applicationswhere it is necessary to remove minute particles from a gas.

The precipitator 10 comprises generally a pair of electrodes 14 and 16disposed in the stream of the gas, the electrodes being connected to asuitable high potential source 39 as shown in FIG. 7. The high potentialbetween the electrodes creates a corona discharge that places anelectrical charge on the particles passing between the electrodes. Dueto the electric field established by electrodes, forces are exerted onthe particles that accelerate them to one of the electrodes, usuallytermed the collecting electrode. Once in contact with the collectingelectrode, which is usually grounded, the particles discharge and remainon the surface of the electrode.

While in FIG. 1 the precipitator 10 is the Cottrell or single stagetype, the present invention is equally applicable to the two stageprecipitator. In the single stage precipitator the same electrodescreate the corona discharge and the electric field that accelerates theparticles to the electrode. On the otherhand, in a two stageprecipitator, separate electrodes create the corona discharge and theelectric field.

The precipitator 10 includes a plurality of corona electrodes 14 and aplurality of collecting electrodes 16. The corona electrodes 14 arearranged in groups of planar arrays 14a, 14b, 14c, 14d and 14e.Preferably, planar arrays 14a, 14c and Me are disposed horizontally inthe stream of the gas, while planar arrays 14b and 14d are disposedvertically. Each of the wires 14 is connected to a high potential sourceshown in FIG. 7. A conductive strip 15 provides a common electricalconnection to the wires of the array 14b and like strips (not shown) aresimilarly used for the other arrays. Also the arrays are held rigid intheir positions by supports (not shown). The wires 14 are preferably ofsmall diameter so that each wire has a relatively small surface area.

A plurality of collecting plates 16 pass through the midplane betweenadjacent arrays of wire. The plates 16 are mounted at their ends to apair of roller chains 18 and 19. The roller chains in turn mesh withteeth 20 of a plurality of sprocket wheels. Roller chain 18 is supportedby upper sprocket wheels 22a, 24a and 26a, middle sprocket wheels 28aand 30a and lower sprocket wheels 32a and 34a. In similar manner, rollerchain 19 is supported by upper sprocket wheels 22b, 24b and 26b, a pairof middle sprocket wheels (not shown in FIG. 1) and a pair of lowersprocket wheels (not shown in FIG. 1). The sprocket wheels are in turnmounted on a support rod, such as a rod 36. A drive mechanism, such as amotor 37, imparts motion to the plates 16 around and between the arraysof wire 14 by imparting rotary motion to the sprocket wheels.

The plates 16 are preferably rectangular in shape. The longest dimension38 extends parallel to the direction of gas flow and the shorterdimension 40 is parallel to the direction of movement of the plates 16.The surface area of the plates 16 is preferably substantially largerthan the surface area of the wires 14. The plates 16 are metallic andpreferably grounded as shown functionally at 42. Each of the plates 16is separated from adjacent plates by a spacing 44. Additionally, theplates 16 are preferably rigid, and therefore, when the plates passaround the sprocket wheels, as at 46, the plates maintain their flatsurface unlike the known unitary metallic sheet electrodes. Both sidesof the collecting plates 16 collect the particles.

Preferably, the plates 16 are fastened to the roller chains 18 and 19 ata point approximately midway between the dimension 40 of the plates 16to permit the ends of the plates 16 to spread out a distance from theroller chain during rotation about the sprockets as at 46. One suitablefastener is the assembly shown in FIG. 3 at 47. The fastener shouldpermit the plates to be readily assembled and removed.

The optimum size of the plates 16 and the spacing therebetween is afunction of several factors. First, it is desirable to make the overallsurface area on one hand as close as possible to that of a continuousmetallic belt to provide maximum surface area for collecting particles.Thus, the dimension 38 is relatively large to accommodate this feature.The spacing 44 need be no larger than is necessary to prevent the plates16 from contacting each other, especially as the sprockets pass over thesprocket wheels. The size of the dimension 40 is related somewhat to thediameter of the sprocket wheels; the dimension should not be so small asto deviate too far from the feature of maximizing surface area and yetshould not be so large as to cause the plate to undergo extreme, erraticmotion as the plate passes around the sprocket wheel. Preferably, thedimension is approximately the size of the radius of the sprocket wheel.

In keeping with one of the desirable features of a moving collectingelectrode, the electrode passes out of the gas stream and into a region,represented generally by a housing 48, where the electrode is cleaned.Thus, this arrangement permits the particles that are removed from theelectrode from becoming re-entrained in the gas. In the presentinvention, each plate 16 is individually cleaned by any of severalcleaning arrangements, shown in FIGS. 8a to 8e. The plates 16 enter thehousing 48 through a slot (not shown in FIG. 1) and leave through aslotted opening 50 for a belt movement shown by an arrow 52.

Several cleaning arrangements may be used either alone or incombination. Referring now to FIG. 8a, the plates 16 may be individuallycleaned by a pair of rotating brushes 53a and 53b that come into contactwith the plates as they pass through the housing 48. In FIG. 8b aheating device 55 heats the plates 16 to assist in removing theparticles from the plates. In FIG. a mechanical vibrator 57 impartsvibratory motion to the plates. Referring to FIG. 8d, a plurality ofjets 59 direct air under pressure to the surface of the plates.Preferably, the jets 59 are in combination with the brushes 53a and 53b.Lastly, FIG. 8e shows a plurality of devices 61 that direct liquid inturbulent, active or sonic motion against the plate surfaces.

Another feature of the present invention resides in the ease of repairor replacement of the plates 16. A maintenance section, represented inFIG. 1 by a housing 54, permits access to any of the plates 16. Thehousing 54 has a removable cover (not shown) whereby access may bepermitted to the plates within the housing. Thus, the precipitator needbe shut down only while the defective plate is removed and replaced byanother. With precipitators having a unitarybelt, the precipitator mustbe shut down until the belt is repaired.

Preferable, the surfaces of the collecting plates are provided withraised and depressed areas as shown in FIGS. 2 to 6 and FIGS. 9 to 12.These areas assist the particle collection process in several ways. Thedepressed areas form shields or shadow zones where the particles maycollect without being re-entrained by the scouring action of the gasstream. In addition, the raised and depressed areas produce a region inthe depressed areas where the electric field for particle collection islow. Charged particles tend to steer into low field regions.

In FIG. 2, rows and columns of alternate, square raised and depressedareas 60 and 62, respectively, are formed on the surface of the plate16. The comers of the areas are preferably rounded, as at 64, tofacilitate cleaning the plates.

Similarly, in FIG. 3 the surface of the plate 16 has circular depressedareas 66 and circular raised areas 68.

In FIG. 4a raised and depressed areas 70 and 72, respectively, arerectangular shaped with rounded corners. The longer dimension isparallel to the longer side 38 of the plate 16. The rectangular shapedareas may however be formed with the longer dimension parallel to theshorter side 40 of the plate 16 as shown in FIG. 41;.

Referring now to FIG. 5, the plate 16 comprises a web 74 with a pair ofend flanges 76 and 78 formed generally perpendicular to the web 74.Preferably, the plate 16 is affixed to the roller chains 18 and 19 atthe midpoint of the web 74 by a suitable fastener.

Similarly, FIG. 6 has a web 80 with flanges 82, 84, 86 and 88 disposedat a right angle to the web 80.

The collecting plate in FIG. 9 includes a plate 90 and a series of sidemembers 92 and 94. The side members 92 and 94 extend from the plate 90at an acute angle to form a region 96 and a region 98 that is protectedform the moving gas stream represented by an arrow 100. These regions 96and 98 also have a low electric field, and thus, the charged particlesare attracted to them. I

In FIG. the collecting plate includes a flange 102, a flange 104 and anundulated web 106. The undulated web 106 increases the anode area forcollecting particles in addition to creating collecting regions removedfrom high gas flow and from high collecting electric fields.

In FIG. 1 1 a collecting plate 108 is formed with a series of holes 1 10extending through the thickness of the plate. Preferably, the diameterof the holes ranges from 1 to 3 times the plate thickness shown at 112.

Lastly, the collecting plate of FIG. 12 is formed as a hollow tube 1 14with a plurality of holes 1 16. The holes 116 pass through the thicknessof the sides of the tube 114. As shown in FIG. 12 the holes 110 arepresent on each active side of the tube. The total hole area ranges from25% to of the plate area on that side and preferably is 50% of the platearea on that side. Also, in FIG. 12, the holes on opposite sides of thetube 114 do not line up.

The advantages of the present invention are realized in all of theembodiments herein described. The primary advantage resides in thereduction of reentrainment of the particles in the gas flow once theyare accumulated on the collecting electrode. One feature which permitsthis advantage is that the collecting electrode moves to a separateelectrode cleaning area and is fonned as a series of separate platesthat are individually cleaned. Furthermore, the collecting plates havesurface geometries that have areas that are removed from the gas flow,thereby further reducing reentrainment. In addition, these areas havegenerally weak electrostatic fields which cause the particles to migratetoward them.

The embodiments of the present invention are intended to be merelyexemplary and those skilled in the art shall be able to make numerousvariations and modifications to them without departing from the spiritof the invention. All such variations and modifications are intended tobe within the scope of the invention as defined by the claims.

We claim:

I. An electrostatic precipitator including a housing having fluid inletand outlet means, electrode inlet and outlet means, a plurality ofplanar arrays of wire positioned in the stream of fluid containingparticles within said housing, a plurality of metallic plates ofgenerally rectangular shape, the shorter dimension of which beingdisposed parallel to the direction of movement of the plates, the longerdimension of which being disposed perpendicular to the direction ofmovement of the plates, positioned adjacent to one another and adaptedto be positioned between the arrays of wire, the plates forming acollecting electrode having multiple raised and depressed portions onthe surface of the plates forming alternately open topped, open bottomenclosed areas for creating regions of dimension smaller than those ofthe plate which have reduced electric fields to enhance particlecollection therein and which are shielded from the fluid stream toreduce re-entrainment of the collected particles, means for producing acorona discharge between the arrays of the wire and the collectingelectrode, and means connected successively to the shorter dimension ofeach of the plates of the collecting electrode for moving the platesaround an endless path formed by said electrode between successivearrays of wire and extending outside said housing through said electrodeinlet and said electrode outlet means provided therein.

2. The precipitator according to claim 1 wherein the plates areseparated from adjacent plates so that they do not touch.

3. The precipitator according to claim 1 including means associateddirectly with said plates and said means for moving said platesconnecting said plates to said moving means such that said plates may bereplaced individually.

4. In an electrostatic particle precipitator of the type having ahousing containing a fluid inlet and a fluid outlet, a plurality ofmetallic planar electrodes of relatively large surface area at groundpotential positioned parallel to each other and parallel to the fluidflow within said housing, a plurality of planar arrays of wire ofrelatively small surface area positioned in the respective midplanesbetween adjacent planar electrodes, and means connected to the arraysfor subjecting the same to high corona-producing potentials, wherebyparticles entrained in the gasses flowing between the arrays of theelectrodes are electro-mechanically deposited upon said planarelectrodes, an improvement wherein the planar electrodes are formed intoan articulated endless belt, the belt including a plurality of separatesmetal strips of extended length in the direction of gas flow and ofshort width in the direction of belt travel, each strip having multipleraised and depressed portions of dimension smaller than those of thesurface of the strip on the surface of the strip forming alternatelyopen topped, open bottom enclosed areas for creating regions which havereduced electric field to enhance particle collection therein and whichare shielded from the gas flow, each strip being mechanically connectedat each short end thereof to an endless, linked roller chain to form analmost closed surface, said chains being engaged by an arrangement ofsupported lower sprockets, means for moving the strips successivelybetween at least three planar wire arrays at high potential and thenceto a region separated from said corona and said flowing gasses, andmeans in said region for removing successively from each strip theparticles adherent to its surface, whereby re-entrainment in the gasflow of particle accumulations from the grounded electrodes is reduced.

5. The precipitator according to claim 1 wherein each strip has a fixedalignment with respect to the portion of the chain to which it isattached.

6. An electrostatic particle precipitator including a housing havingfluid inlet and outlet means, electrode inlet and outlet means, aplurality of planar arrays of wire positioned in the stream of fluidcontaining particles within said housing, a plurality of metallic platesof generally rectangular shape, the shorter dimension of which beingdisposed parallel to the direction of movement of the plates, the longerdimension of which being disposed perpendicular to the direction ofmovement of the plates, positioned adjacent to one another and adaptedto be positioned between the arrays of wire, the plates forming acollecting electrode and having multiple raised and depressed areas ofalternately open top, open bottom rectangular box shape on the surfaceof the plates for creating regions of dimensions smaller than those ofthe plates which have reduced electric fields to enhance particlecollection therein and which are shielded from the fluid stream toreduce reentrainment of the collected particles, means for producing acorona discharge between the arrays of wire and the collectingelectrode, and means connected successively to the shorter dimensioneach of the plates of the collecting electrode for moving the platesaround an endless path formed by said electrode between successivearrays of wire and extending outside said housing through said electrodeinlet and electrode outlet means provided therein.

7. The precipitator according to claim 6 wherein said multiple raisedand depressed areas are of alternately open top, open bottom cylindricalshape.

1. AN ELECTROSTATIC PRECIPITATOR INCLUDING A HOUSING HAVING FLUID INLETAND OUTLET MEANS, ELECTRODE INLET AND OUTLET MEANS, A PLURALITY OFPLANAR ARRAYS OF WIRE POSITIONED IN THE STREAM OF FLUID CONTAININGPARTICLES WITHIN SAID HOUSING, A PLURALITY OF METALLIC PLATES OFGENERALLY RECTANGULAR SHAPE, THE SHORTER DIMENSION OF WHICH BEINGDISPOSED PARALLEL TO THE DIRECTION OF MOVEMENT OF THE PLATES, THE LONGERDIMENSION OF WHICH BEING DISPOSED PERPENDICULAR TO THE DIRECTION OFMOVEMENT OF THE PLATES, POSITIONED ADJACENT TO ONE ANOTHER AND ADAPTEDTO BE POSITIONED BETWEEN THE ARRAYS OF WIRE, THE PLATES FORMING ACOLLECTING ELECTRODE HAVING MULTIPLE RAISED AND DEPRESSED PORTIONS ONTHE SURFACE OF THE PLATES FORMING ALTERNATELY OPEN TOPPED, OPEN BOTTOMENCLOSED AREAS FOR CREATING REGIONS OF
 2. The precipitator according toclaim 1 wherein the plates are separated from adjacent plates so thatthey do not touch.
 3. The precipitator according to claim 1 includingmeans associated directly with said plates and said means for movingsaid plates connecting said plates to said moving means such that saidplates may be replaced individually.
 4. In an electrostatic particleprecipitator of the type having a housing containing a fluid inlet and afluid outlet, a plurality of metallic planar electrodes of relativelylarge surface area at ground potential positioned parallel to each otherand parallel to the fluid flow within said housing, a plurality ofplanar arrays of wire of relatively small surface area positioned in therespective midplanes between adjacent planar electrodes, and meansconnected to the arrays for subjecting the same to high corona-producingpotentials, whereby particles entrained in the gasses flowing betweenthe arrays of the electrodes are electro-mechanically deposited uponsaid planar electrodes, an improvement wherein the planar electrodes areformed into an articulated endless belt, the belt including a pluralityof separates metal strips of extended length in the direction of gasflow and of short width in the direction of belt travel, each striphaving multiple raised and depressed portions of dimension smaller thanthose of the surface of the strip on the surface of the strip formingalternately open topped, open bottom enclosed areas for creating regionswhich have reduced electric field to enhance particle collection thereinand which are shielded from the gas flow, each strip being mechanicallyconnected at each short end thereof to an endless, linked roller chainto form an almost closed surface, said chains being engaged by anarrangement of supported lower sprockets, means for moving the stripssuccessively between at least three planar wire arrays at high potentialand thence to a region separated from said corona and said flowinggasses, and means in said region for removing successively from eachstrip the particles adherent to its surface, whereby re-entrainment inthe gas flow of particle accumulations from the grounded electrodes isreduced.
 5. The precipitator according to claim 1 wherein each strip hasa fixed alignment with respect to the portion of the chain to which itis attached.
 6. An electrostatic particle precipitator including ahousing having fluid inlet and outlet means, electrode inlet and outletmeans, a plurality of planar arrays of wire positioned in the stream offluid containing particles within said housing, a plurality of metallicplates of generally rectangular shape, the shorter dimension of whichbeing disposed parallel to the direction of movement of the plates, thelonger dimension of which being disposed perpendicular to the directionof movement of the plates, positioned adjacent to one another andadapted to be positioned between the arrays of wire, the plates forminga collecting electrode and having multiple raised and depressed areas ofalternately open top, open bottom rectangular box shape on the surfaceof the plates for creating regions of dimensions smaller than those ofthe plates which have reduced electric fields to enhance particlecollection therein and which are shielded from the fluid stream toreduce re-entrainment of the collected particles, means for producing acorona discharge between the arrays of wire and the collectingelectrode, and means connected successively to the shorter dimensioneach of the plates of the collecting electrode for moving the platesaround an endless path formed by said electrode between successivearrays of wire and extending outside said housing through said electrodeinlet and electrode outlet means provided therein.
 7. The precipitatoraccording to claim 6 wherein said multiple raised and depressed areasare of alternately open top, open bottom cylindrical shape.